1. Field of the Invention
The present invention generally relates to an abrasive wire for a wire saw and, more particularly, to an abrasive wire having resin-bonded abrasive grains for cutting a hard, brittle material such as a silicon ingot, crystal, quartz or a metal.
2. Description of the Related Art
An abrasive wire saw is known as a cutting tool for cutting a hard, brittle material such as a silicon ingot, crystal, quartz or a metal. Recently, the abrasive wire saw has attracted attention as a cutting tool especially for cutting a silicon ingot to prepare a large diameter silicon wafer used for manufacturing semiconductor devices. Conventionally, an inner-blade disc saw has been used for cutting a silicon ingot. The diameter of the inner-blade disc saw has become larger and larger as the diameter of the silicon wafer formed from a silicon ingot has been increased.
However, there is a limitation to increasing the diameter of the inner-blade disc saw. That is, if the diameter of the inner-blade disc saw is increased to cut a silicon ingot having a diameter of more than 8 inches, there are problems in that: there is a limitation in increasing the throughput; the kerf loss is large; and it is difficult to attach the inner-blade disc saw to a cutting jig. Accordingly, the method for cutting a silicon ingot using the inner-blade disc saw has been replaced by a multi wire cutting method.
FIG.1 shows a structure of a conventional wire cutting apparatus for cutting a silicon ingot using the multi wire cutting method. The wire cutting apparatus shown in FIG. 1 uses a wire 1 such as a piano wire. The wire 1 is supplied from a new wire reel 2 and is wound on a winding roller 5. Between the new wire reel 2 and the winding roller 5, the wire 1 is engaged with dancer rollers 3 and a plurality of main rollers 4. The wire 1 forms a plurality of parallel lines having a predetermined pitch therebetween by being engaged with the main rollers 4 as shown in FIG. 1. An abrasive slurry having a high viscosity is supplied onto the wire 1 from slurry nozzles 7 so that the abrasive slurry adheres to the wire 1 forming the parallel lines. A silicon ingot 6 is pressed against the wire 1 while the wire 1 is moving and the abrasive slurry is being supplied onto the wire 1. Thus, the silicon ingot is cut by the abrasive slurry adhering to the wire 1.
The above-mentioned cutting method has the following problems due to the abrasive slurry which must be disposed of as industrial waste:
1) a large amount of industrial waste is generated;
2) the working environment is extremely bad;
3) operating costs are high;
4) it is difficult to clean the silicon wafers after being cut;
5) it is difficult to increase cutting efficiency; and
6) accuracy of cutting is low.
In order to solve the above-mentioned problems, an electrodeposition abrasive wire which comprises abrasives attached to a core wire has been developed. Such an abrasive wire is disclosed in Japanese Laid-Open Patent Applications No. 63-22275, No. 4-4105, No.7-227767 and No. 9-150314. Additionally, an abrasive wire having abrasives mechanically embedded in a wire material is disclosed in Sumitomo Electric Company Report, 1988 March, Vol. 132, pp.118-122. These abrasive wires use a metal to bond abrasive grains to a core wire.
However, the abrasive wire using a metal as a bonding material has low strength with respect to torsion and bend since the bonding material layer is hard. Accordingly, such an abrasive wire can be easily cut. Additionally, the manufacturing cost of the electrodeposition abrasive wire is high since it takes a long time to bond the abrasives by electrodeposition. Further, the abrasive wire cannot be made long enough for the multi wire cutting method. In order to eliminate the problem related to the length of the abrasive wire, an endless type abrasive wire made by joining opposite ends of a short wire has been suggested. However, there is a problem in that such an endless type abrasive wire has extremely low strength with respect to torsion and bend.
In order to solve the above-mentioned problems, an abrasive wire using a resin as a bonding material has been developed. Such a resin bonded abrasive wire and a manufacturing method thereof is disclosed in xe2x80x9cCutting Performances of Bonded Abrasives type Diamond Wire Sawxe2x80x9d, The Society of Grinding Engineers 1997 Symposium Proceedings, pp.369-370. Such a resin bonded abrasive wire is also disclosed in Japanese Laid-Open Patent Applications No. 8-126953, No. 9-155631, No. 10-138114, No. 10-151560, No. 10-315049, No. 10-328932 and No. 10-337612. None of the literature or the patent documents refers to the type of resin to be used to bond the abrasives. However, according to their contents of disclosure and embodiments described therein, the resin is supposed to be a thermosetting resin such as a phenol resin, which has been used for grinding wheels.
However, in the above-mentioned improved abrasive wire, a drying process for removing solvent from the bonding material and a thermal curing process for curing the bonding material are needed since a thermosetting resin is used as the bonding material. The time period required for the thermal curing process is a few minutes for each part of the abrasive wire.
Additionally, Japanese Laid-Open Patent Application No. 11-48035 discloses an abrasive wire using a ceramic to bond abrasive grains so as to increase holding strength of the abrasive grains. However, the temperature for forming such a ceramic bonding layer is very high and a time period for forming the ceramic bonding layer is a few minutes.
Accordingly, it is difficult to fabricate the resin bonded abrasive wire or the ceramic bonded abrasive wire at speeds in the range of a few hundred meters per minute to a few kilometers per minute. Thus, it is very difficult to fabricate the resin bonded abrasive wire or the ceramic bonded abrasive wire having a length of more than 10 kilometers, which is required for the multi wire cutting method, at a low cost.
Additionally, the resin bonded abrasive wire is inferior to the metal bonded abrasive wire with respect to the abrasion resistance, mechanical strength, heat resistance and cutting ability.
It is a general object of the present invention to provide an improved and useful abrasive wire and a manufacturing method thereof in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an abrasive wire which provides an efficient cutting operation with high accuracy and a long service life.
Another object of the present invention is to provide an abrasive wire which can be made long enough for the multi wire cutting method at a low manufacturing cost.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention an abrasive wire comprising: a core wire; abrasive grains provided around the core wire; and a bonding layer formed on the core wire so as to bond the abrasive grains to the core wire, the bonding layer being formed by a light curing resin.
According to the above-mentioned invention, the time period for manufacturing the abrasive wire can be reduced since the light curing resin can be cured in a very short time. The mechanical strength and heat resistance of the abrasive wire can be increased by adding a filler such as inorganic particles or fibers to the bonding layer. Additionally, the adhesion of the bonding layer can be increased by providing a primer to the core wire prior to the formation of the bonding layer, thereby increasing the service life of the abrasive wire.
The bonding layer may include a plurality of layers each of which is made of a light curing resin having different characteristic. That is, a first layer contacting the core wire may be made of a light curing resin adhesive layer having adhesive force stronger than the light curing resin forming other layers. By adding the abrasive particles to the first layer, the abrasive particles can be securely bonded to the core wire. Additionally, the outermost layer may be made of a light curing resin having abrasion resistance.
Additionally, there is provided according to another aspect of the present invention a method for manufacturing an abrasive wire, comprising the steps of: applying a light curing resin liquid to a core wire while the core wire is moved in the direction of the longitudinal axis of the core wire, the light curing resin liquid containing abrasive grains; and curing the light curing resin liquid adhering to the core wire by projecting a light on the light curing resin liquid while the core wire is moved in the direction of the longitudinal axis of the core wire so as to bond the abrasive grains to the core wire.
According to this invention, the light curing resin is used for bonding the abrasive grains to the core wire. Since the light curing resin can be cured within a few seconds, the curing operation can be performed while the core wire is moved in the direction of the longitudinal axis of the core wire. Accordingly, a long abrasive wire can be fabricated at reduced time and cost.
Additionally, there is provided according to another aspect of the present invention an abrasive wire comprising: a core wire; abrasive grains provided around the core wire; and a bonding layer formed on the core wire so as to bond the abrasive grains to the core wire, the bonding layer being formed by an electron beam curing resin.
According to the above-mentioned invention, a time period for manufacturing the abrasive wire can be reduced since the electron beam curing resin can be cured in a very short time. The mechanical strength and heat resistance of the abrasive wire can be increased by adding a filler such as inorganic particles or fibers to the bonding layer. Additionally, the adhesion of the bonding layer can be increased by providing a primer to the core wire prior to the formation of the bonding layer, thereby increasing the service life of the abrasive wire.
The bonding layer may include a plurality of layers each of which is made of an electron beam curing resin having different characteristic. That is, a first layer contacting the core wire may be made of an electron beam curing resin adhesive layer having adhesive force stronger than the electron beam curing resin forming other layers. By adding the abrasive particles to the first layer, the abrasive particles can be securely bonded to the core wire. Additionally, the outermost layer may be made of a light curing resin having abrasion resistance.
Additionally, there is provided according to another aspect of the present invention a method for manufacturing an abrasive wire, comprising the steps of: applying an electron beam curing resin liquid to a core wire while the core wire is moved in a direction of a longitudinal axis of the core wire, the electron beam curing resin liquid containing abrasive grains; and curing the electron beam curing resin liquid adhering to the core wire by projecting an electron beam on the light curing resin liquid while the core wire is moved in the direction of the longitudinal axis of the core wire so as to bond the abrasive grains to the core wire.
According to this invention, the electron beam curing resin is used for bonding the abrasive grains to the core wire. Since the electron beam curing resin can be cured within one second, the curing operation can be performed while the core wire is moved in the direction of the longitudinal axis of the core wire. Accordingly, a long abrasive wire can be fabricated at reduced time and cost.
Other objects, features and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings.